Extremely high levels of regiochemical control were achieved in this process. For example, when keto aldehydes (1 and 2, R4= H) were used in the annulation reaction, a single regioisomeric bicyclic ether was obtained. Even when diketone substrates were employed, good to very good regiochemical control was obtained depending on the ketone substituents. In all cases, the observed products 4 and 6 resulted from initial attack of the ...